1. Field of the Invention
Aspects of the present invention relate to a line interface unit of a multifunction printer, and more particularly, to a line interface unit of a multifunction printer in which duplicated parts of a circuit to detect a calling line and a circuit to detect a ring signal is improved and easily implemented.
2. Description of the Related Art
A multifunction printer having functions of scanning an image and transmitting and receiving fax data, which are added to a printer, is being developed. In order to perform a facsimile function in the multifunction printer, a communication line is formed using a telephone connecting apparatus to connect the multifunction printer to a public switched telephone network.
As illustrated in FIG. 1, a conventional telephone connecting apparatus of a multifunction printer includes a public switched telephone network 10, a line interface unit/connecting unit (LIU), a facsimile modem 40 to transmit and receive fax data, an audio outputting unit 50 to output a ring signal, a central controller (CPU) 70, an image reader 90 to scan and provide an image to the central controller 70, and a manipulating panel 80. The manipulating panel 80 may include a key manipulating unit for a user to input a command and a liquid crystal display (LCD) to display operating state and setting state.
The connecting unit LIU includes a line property controller 20, a line switch SW, a calling line detecting unit 30, and a ring signal detecting unit 60. The line property controller 20 is connected to the public switched telephone network 10 and to the facsimile modem 40 through a data line DL. The switch SW changes between a first contact a and a second contact b. In an ON-Hook mode, the line switch SW contacts the first contact a and is set to an idle mode. In the OFF-Hook mode, the line switch SW contacts the second contact b, is set to a handset mode.
The calling line detecting unit 30 is connected between the public switched telephone network 10 and the facsimile modem 40. The calling line detecting unit 30 detects a calling line to be transmitted from the public switched telephone network 10 at the idle mode to provide the detected calling line to the facsimile modem 40. The facsimile modem 40 identifies the detected calling line and provides information of the calling line to the central controller 70.
The ring signal detecting unit 60 is connected between the public switched telephone network 10 and the central controller 70. The ring signal detecting unit 60 detects the ring signal transmitted from the public switched telephone network 10 at the idle mode to provide the detected ring signal to the central controller 70. The central controller 70 notifies the ring signal to the facsimile modem 40 when receiving the detected ring signal such that the audio outputting unit 50, connected to the facsimile modem 40, audibly outputs the ring signal.
When the number of times of detecting the ring signal reaches a predetermined number of times, a facsimile receiving mode of receiving the facsimile data is set. At this time, the facsimile modem 40 receives the facsimile data through the data line DL. After the facsimile data is received prints the received data is printed using a printer driving unit (not shown) controlled by the central controller 70.
The calling line detecting unit 30 includes a transformer TS to electrically separate a primary coil connected to the public switched telephone network 10 from a secondary coil connected to the facsimile modem 40. The primary coil of the transformer TS is connected in series to a first capacitor C1 and a first resistor R1 to match the impedance of the telephone/calling line. The secondary coil of the transformer TS is connected in parallel to diodes D1 and D2 to prevent a surge voltage. The diodes D1 and D2 are connected in parallel to a capacitor C11 to remove noise and a resistor R11 to match the input impedance.
The ring signal detecting unit 60 includes a phototransistor 61 having a primary side and a secondary side, the primary side being electrically separated from the secondary side. The primary side is connected to the public switched telephone network 10 and the secondary side is connected to the central controller 70. A light emitting port of the phototransistor 61 is connected in series to a second capacitor C2 and a second resistor R2 to match the impedance of the telephone/calling line. A light receiving port of the phototransistor 61 is connected to a resistor R21 and a capacitor C21 to change a signal waveform such that the central controller 70 can exactly recognize the ring signal.
According to the conventional line interface unit (LIU) of the multifunction printer, the input sides of the calling line detecting unit 30 and the ring signal detecting unit 60 are connected to the public switched telephone network 10, but the output sides thereof are individually connected to the facsimile modem 40 and the central controller 70, respectively. Since the calling line detecting unit 30 and the ring signal detecting unit 60 have a similar structure in view of electrically insulating the input sides and the output sides along the reference lines Z-Z and share the input sides thereof, it is required to improve the structure duplicated due to the similar components for a simpler structure.